Proton therapy delivery method affects dose-averaged linear energy transfer in patients

Image-based data mining applies to data collected from children

PURPOSE

Image-based data mining (IBDM) is a novel voxel-based method for analyzing radiation dose responses that has been successfully applied in adult data. Because anatomic variability and side effects of interest differ for children compared to adults, we investigated the feasibility of IBDM for pediatric analyses.

METHODS

We tested IBDM with CT images and dose distributions collected from 167 children (aged 10 months to 20 years) who received proton radiotherapy for primary brain tumors. We used data from four reference patients to assess IBDM sensitivity to reference selection. We quantified spatial-normalization accuracy via contour distances and deviations of the centers-of-mass of brain substructures. We performed dose comparisons with simplified and modified clinical dose distributions with a simulated effect, assessing their accuracy via sensitivity, positive predictive value (PPV) and Dice similarity coefficient (DSC).

RESULTS

Spatial normalizations and dose comparisons were insensitive to reference selection. Normalization discrepancies were small (average contour distance < 2.5 mm, average center-of-mass deviation < 6 mm). Dose comparisons identified differences (p < 0.01) in 81% of simplified and all modified clinical dose distributions. The DSCs for simplified doses were high (peak frequency magnitudes of 0.9-1.0). However, the PPVs and DSCs were low (maximum 0.3 and 0.4, respectively) in the modified clinical tests.

CONCLUSIONS

IBDM is feasible for childhood late-effects research. Our findings may inform cohort selection in future studies of pediatric radiotherapy dose responses and facilitate treatment planning to reduce treatment-related toxicities and improve quality of life among childhood cancer survivors.

Pre- and Post-therapy Risk Factors for Vasculopathy in Pediatric Craniopharyngioma Patients Treated with Surgery and Proton Radiotherapy

PURPOSE

Vasculopathy (VAS) is a significant complication associated with radiotherapy in patients treated for brain tumors. We studied the type, location, severity, timing, and resolution of VAS in children with craniopharyngioma treated with proton radiotherapy (PRT) and evaluated predictors of stenosis (STN) using a novel patient and imaging-based modelling approach.

MATERIALS/METHODS

Children with craniopharyngioma (N=94) were treated with 54 GyRBE PRT on a clinical trial NCTXXXXXXXX.¹ We evaluated VAS type, location, severity, and resolution. VAS events were segmented and related to their location, operative corridor, PRT dose, and vascular territory to facilitate Mixed Effect Logistic Regression Modelling of spatial predictors of STN events.

RESULTS

Forty-five (47.9%) patients had 111 instances of confirmed VAS (pre-PRT N = 37, 33.3%). The median time to post-PRT VAS was 3.41 years (95% CI 1.86-6.11). Stenosis events were observed post-PRT in 23.4% (N=22) patients. Post-PRT VAS was detected by cerebral angiogram in 9.6% (N=9), severe in 4.3% (N=4), and compensated on perfusion in 2.1% (N=2). Revascularization was required for 5 (5.3%) patients. Post-surgical, pre-PRT VAS, and PRT dose to unperturbed vessels were predictive of STN. The impact of PRT on STN was negligible within the surgical corridor.

CONCLUSIONS

VAS often precedes PRT and was the strongest predictor of post-PRT STN. The adverse impact of PRT on STN was only apparent in unperturbed vasculature beyond the operative corridor.